The invention relates to a screw cap for containers, particularly beverage bottles, with a closure member and a circular guarantee strip connected thereto by means of a plurality of webs and by means of a connecting piece and at the time of the first unscrewing of the cap from the closure member, said strip is at least partly separated and at least the guarantee strip is made from heat shrinkable plastic.
Guarantee strips on caps, tops, closures and the like serve to indicate the first unscrewing of the cap or the opening of the container. This is indicated by the fact that the guarantee strip is damaged during the opening process. Generally, there is a clearly visible separation from the actual cap. Such guarantee strips are in particular known in connection with metal screw caps, in which they remain attached to the container neck as a separated ring. However, strips made from paper and plastic have also already been proposed.
The choice of the most suitable type of guarantee strip in the case of containers, depends on the possibilities of reusing the latter. More particularly in the case of bottles, it is a question of whether they are so-called disposable bottles, or whether they are returned to the filling station for reuse. In the latter case, certain important points must be taken into consideration and which result from the rational reuse of such bottles, although they are generally ignored. It is firstly and particularly important that following the initial opening and its separation from the cap, the guarantee strip does not remain attached to the bottle. This is unimportant in the case of disposable bottles, but with bottles which are returned it must be remembered that on return these bottles are cleaned, the label is removed, they are then filled and provided with a new and identical cap. However, the cleaning installations are unable to remove guarantee strips which remain attached. In view of the high hourly capacity of such plants, the fitting of the new cap can lead to serious faults. This is particularly the case when using the caps having guarantee strips made from heat shrinkable plastic.
Heat shrinkable caps for beverage bottles are already known. In the case of such a cap, below the cap body there is merely a thin ring, which is connected to the said body by means of thin webs and a single connecting piece. Although the lower end of the ring extends up to the container neck, its upper edge still remains on the threaded mouth area, whose diameter is somewhat larger than that of the neck. This diameter difference makes it possible to shrink the guarantee strip onto the smaller diameter of the neck, although it initially has a diameter corresponding to that of the mouth area. If shrinkage is inadequate, the lower edge does not correctly engage on the neck and there is a risk that the screw cap can be removed from the bottle without damaging the guarantee ring. However, if more shrinkage heat is applied to the closure, there can be peripheral bonding together of the ring as a result of the disappearance of the inadequate predetermined breaking point due to material flow. However, as a result of this bonding or sealing operation, the ring sticks to the bottle, because it has now become resistant to expansion, leading to the disadvantages referred to hereinbefore.